Existing light emitting diodes (“LEDs”) can emit light in the ultraviolet (“UV”), visible or infrared (“IR”) wavelength range. These LEDs generally have narrow emission spectrum (approximately +/−10 nm). As an example, a blue InGaN LED may generate light with wavelength of 470 nm+/−10 nm. As another example, a green InGaN LED may generate light with wavelength of 510 nm+/−10 nm. As another example, a red AlInGaP LED may generate light with wavelength of 630 nm+/−10 nm.
However, in some applications, it is desirable to use LEDs that can generate broader emission spectrums to produce desired color light, such as white light. Due to the narrow-band emission characteristics, these monochromatic LEDs cannot be directly used to produce broad-spectrum color light. Rather, the output light of a monochromatic LED must be mixed with other light of one or more different wavelengths to produce broad-spectrum color light. This can be achieved by introducing one or more fluorescent materials into the lamp of a monochromatic LED to convert some of the original light into longer wavelength light through fluorescence. The combination of original light and converted light produces broad-spectrum color light, which can be emitted from the LED as output light. The most common fluorescent materials used to create LEDs that produce broad-spectrum color light are fluorescent particles made of phosphors, such as Garnet-based phosphors, Silicate-based phosphors, Orthosilicate-based phosphors, Sulfide-based phosphors, Thiogallate-based phosphors and Nitride-based phosphors. These phosphor particles are typically mixed with the transparent material used to form the lamps of LEDs so that original light emitted from the semiconductor die of an LED can be converted within the lamp of the LED to produce the desired output light.
A concern with the use of phosphor particles to produce broad-spectrum color output light is that the output light may have a low Color Rendering Index (CRI), which may be as low as sixty-five (65). This is readily apparent by examining the optical spectrum of the output light, which would typically have large gaps or valleys at various wavelengths.
In view of this concern, there is a need for a device and method for emitting broad-spectrum color output light with high CRI.